1. Field of the invention
The invention relates to a method for controlling a beam of light coupled in into an optically conductive working layer, which beam of light is supplied to a working area made of electro-optical material and lying within said working layer. Moreover, the invention relates to an optical control device for controlling a beam of light, and comprising a working layer into which a beam of light to be controlled is coupled in, and at least one working area of electro-optical material, to which the beam of light coupled in is supplied, as well as exciting means for exciting under the control of control means an electric control field in the working area.
2. State of the art
A method respectively a device of the aforesaid type is known from the European patent application EP No. 87200536 (STATE OF THE NETHERLANDS). This publication describes a device for controlling beams of light, in which case such a beam of light is coupled in into a working layer of electro-optical material and is supplied to a working area lying within that working layer. The electro-optical material is a thin film of a polymer dissolved in a volatile solvent, the polymer having a .DELTA.n&gt;0.005 at 1 V/.mu.m, where .DELTA.n represents a change of refractive index n of the electro-optical material caused by the voltage applied to the electro-optic material. The film layer can be applied with a suitably chosen thickness (some .mu.ms) by means of the spinning method. The electro-optical material of the working layer has everywhere one and the same optical axis, perpendicular to the plane of the working layer (id est the material is birefringent, the refractive index for light (ny) polarized in the y-direction--perpendicular to the surface of the working layer--being greater than the refractive index for light (nx) polarized in the x-direction--parallel to the surface of the working layer). An electric control field can be excited in the working area by exciting means (electrodes on both sides of the working area). This field is--just like the optical axis of the working-layer material--(substantially) at right angles to the working layer. When the working area is exposed to the electric control field, the refractive index of the working-layer material inside the working area will get another value than the refractive index of the material outside the working area. Owing to this the working area will form a light waveguide. It will, however, lose that function as soon as the field is removed. In this way the intensity of a beam of light supplied to such a working area is controlled by the electric field. By utilizing more working areas extending parallel to one another optical switches or direction couplers with e.g. two optically conductive states will be obtained: when there is a control field, the parallel working areas will form parallel light waveguides and the beam of light will be transmitted--by optical induction--from the one working area to the other working area; when there is no such field, no light waveguides will be formed and, consequently, the beam of light will not be transmitted.
For some applications the known method respectively device has the drawback that a working area will form a light waveguide only as long as there is the electric control field. After removing the control field the light waveguide will disappear again. Consequently, one of the two optically conductive states of the known device will be non-stationary (to wit when there is the control field); the other one will be quasi-stationary (when there is no control field).